Laminate construction

ABSTRACT

This disclosure relates to a novel method of forming a tear line in a laminated as well as the laminate per se and methodwise incudes the steps of providing a tool having a heated edge, applying the heated edge to a laminate under pressure to effect a heating and flowing of a stiffening layer thereof, and effecting relative movement of the laminate and the tool along a predetermined line to form a weakening line in the stiffening layer. Preferably though not necessarily the article is composed solely of a metal foil layer and a thermoplastic resin stiffening layer with the thermoplastic resin stiffening layer having a weakening line molded in the surface thereof remote from the foil layer.

y 1974 R. D. LURIE 3,812,002

LAMINATE CONSTRUCTION Filed Dec. 6, 1971 \s \s y INVENTOR RANDOLPH D. Lume ATTORNEYS 3,812,002 Patented May 21, 1974 -United States PatentOiiice 3,812,002 LAMINATE CONSTRUCTION Randolph D. Lurie, Park Forest,Ill., assignor to Continental Can Company, Inc., New York, N.Y.

Continuation of abandoned application Ser. No. 379,650, July 1, 1964.This application Dec. 6, 1971, Ser. No.

Int. Cl. B32b 3/00 ABSTRACT OF THE DISCLOSUR This disclosure relates toa novel method of forming a tear line in a laminate as well as thelaminate per se and methodwise includes the steps of providing a toolhaving a heated edge, applying the heated edge to a laminate underpressure to effect a heating and flowing of a stlfiening layer thereof,and effecting relative movement of the laminate and the tool along apredetermined line to form a weakening line in the stiffening layer.

Preferably though not necessarily the article is composed solely of ametal foil layer and a thermoplastic resin stiffening layer with thethermoplastic resin stiffening layer having a weakening line molded inthe surface thereof remote from the foil layer.

The present patent is a continuation of commonly assigned U.S.Application No. 379,650, filed July 1, 1964, in the name of Randolph D.Lurie, entitled Laminate Construction, which is abandoned.

This invention relates in general to new and useful improvements inlaminate constructions, and more particularly to a laminate of metalfoil and plastic.

This invention particularly relates to a novel metal foil to plasticlaminate which is suitable for use in the forming of containers, andwhich laminate may be readily torn along a desired line while prior tothe tearing of the laminate, the integrity of the package is maintained.

A primary object of this invention is to provide a novel laminate whichis suitable for use in the forming of packages wherein the laminate isformed of metal foil and plastic and wherein the packages may be readilyopened by the tearing away of a predetermined portion of the material ofthe package.

Another object of this invention is to provide a novel laminateparticularly adapted for the forming of packages wherein the laminate isreadily tearable along predetermined lines the laminate being formed ofmetal foil and plastic and wherein the plastic is weakened along thepredetermined lines while the metal foil remains undamaged.

Still another object of this invention is to provide a novel laminate ofa metal foil and a plastic, the plastic being of the type wherein it maybe readily heat weakened and the laminate having at least one line ofweakening therealong which has been accomplished by heat weakening theplastic material along that line.

A further object of this invention is to provide a novel laminate whichis formed of a metal foil and a plastic and wherein after the formationof the laminate, the plastic may be suitably scored leaving an exposedmetal foil in the plastic without reducing the barrier properties of thelaminate.

Another object of this invention is to provide a novel laminate which issuitable for use in the forming of packages with the laminate beingimpervious to liquids and having the required strength while at the sametime being readily tearable along a predetermined line to facilitate theopening of the package, the laminate being formed of metal foil and asuitable thermodegradable material wherein the necessary tear line maybe readily defined by applying heat along a concentrated line sufficientto greatly weaken the thermodegradable material while permitting themetal foil to remain intact.

With the above and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims and theseveral views illustrated in the accompanying drawing:

In the drawing.

FIG. 1 is a perspective view of a three-ply laminate formed inaccordance with this invention and having a tear strip defined therein,portions of the laminate being broken away to show the specific detailsof the three plies thereof.

FIG. 2 is an enlarged fragmentary transverse sectional view taken alongthe line 22 through one of the weakening lines of the laminate and showsthe specific details thereof. 1

FIG. 3 is a bottom perspective view of a two-ply laminate formed inaccordance with this invention and having incorporated therein a tearstrip.

FIG. 4 is an enlarged fragmentary sectional view taken along the line4-4 of FIG. 3 and shows the specific details of the laminate along oneof the weakening lines formed therein.

Metal foil to plastic and other inexpensive packaging materialslaminates have been found to be very suitable for use in containermanufacture. Such laminates are relatively inexpensive and showexceptionally good barrier properties. However, such laminates haverelatively high strength and do not tear very readily. As a result, inthe past they have not been suitable for use in the forming ofcontainers due to the difliculties in opening the same.

The normal semi-rigid container is at the present time provided with atear strip. Such a tear strip may be readily formed in paper and likecontainer forming materials by scoring or perforating. The perforatingof a laminate system would destroy the barrier properties of thelaminate system. Also, to score the metal foil of the laminate wouldgreatly reduce the barrier properties of the laminate system. Inaddition, even though the metal foil is scored or entirely cut through,the laminate would still tend to tear in a random manner because of theunweakened plastic or other packaging material layer.

In accordance with this invention, it is proposed to provide a metalfoil to plastic or other thermodegradable packaging material laminatewherein the metal foil is in no way damaged and the laminate is weakenedalong the desired line of tearing by the weakening of the plastic orother thermodegradable packaging material layer. In accordance with thisinvention, this can be accomplished even when the plastic or otherthermodegradable packaging material layer is sandwiched between twometal foil layers.

Referring now to the drawings in detail, it will be seen that there isillustrated in FIG. =1 a typical three-ply laminate formed in accordancewith this invention, the laminate being generally referred to by thenumeral 5. The laminate *5 includes two outer metal foil layers 6 and 7between which there is sandwiched a plastic or other thermodegradablepackaging material layer 8. It is to be understood that the metal foillayers 6 and 7 are suitably T 3 bonded to the layer 8 so as to make arelatively rigid laminate. The manner in which the metal foil islaminated to the layer 8 is in no way a part of this invention and willnot 'be described in detail here.

At this time it is pointed out that the laminate 5 has three primaryrequirements. These, not necessarily in the order of their importance,are as follows:

(1) The layer 8 must be properly bonded to the metal foil layers 6 and7.

(2) The laminate must be economically feasible for the intended use, forexample in containers.

(3) The layer 8 when formed of a thermoplastic material, must fuse at atemperature below the melting point of the metal foil. When the layer 8is formed of a material other than thermoplastic material, it must beformed of a thermodegradable material of a type wherein snf'licientdegradation will take place at a temperature below the melting point ofthe metal foil.

In accordance with this invention, the laminate 5 is provided with twoweakening lines 9 and 10 which define a removable tear strip 11. It isintended that the laminate 5 have suflicient strength for the intendedpurpose and provide a vapor proof barrier. However, in order tofacilitate the opening of a package formed from the laminate 5, it isnecessary that a predetermined section thereof be removable therefrom,and it is for this reason that the tear strip 11 is provided.

It has been found that the tear strip 11 may be readily formed byeffecting a scoring or otherwise weakening of the layer 8 along theweakening lines 9 and 10. This is accomplished with heat fusibleplastics by taking a hot knife and pressing it firmly against the metalfoil layer 6 so as to effect a fusing of the layer 8 when it is formedof a thermoplastic material or the general thermodegradation of thelayer 8 when it is formed of other suitable materials. In order thatthere may be heat transfer through the metal foil layer 6 into the layer8, it is necessary that the heated knife edge be firmly pressed againstthe metal foil layer 6 in order to ensure heat transfer. When the layer8 is formed of a thermoplastic material and the plastic material of theplastic layer 8 is fused, the metal foil layer 6 will be deformed to agenerally V configuration, at 13 in alignment with the weakening line10, as is shown in FIG. 2. Of course, the metal foil layer 6 will alsobe inwardly folded along the weakening line 9, as at 12 shown in FIG. 1.

It is to be understood that in the scoring of the plastic layer 8, it isnecessary that the knife edge utilized in this scoring operation besufficiently hot to transfer heat through the metal foil layer 6 intothe plastic layer 8 and effect a fusing of the plastic material of theplastic layer without melting the metal foil layer 6. When the layer 8is formed of other thermodegradable materials, it is necessary that theheat transferred into the layer 8 be sufficient to effect a charring orother thermodegradation of the material. Also, while force is requiredto firmly place the knife edge in engagement with the metal foil layer6, it is to be understood that the knife is not applied against themetal foil layer 6 with sufficient force to cut or tear the metal foillayer 6.

It has been found that when the laminate 5 is weakened in the mannerdescribed above, it may be readily torn along the weakening line formedtherein. 0n 'the other hand, it has been found that if the metal foillayer or layers are scored or cut, and the layer 8 is not weakened, thenthe tearing of the laminate 5 will not necessarily be along the line ofweakening of the foil layers.

A tear strip formed by the above set forth method has 7 the followingadvantages:

(1) The foil layers are not damaged; therefore, the

. Th tQmQ e f h a n te an thetea strip are quite smooth and not likelyto cause one to cut his or her hands on subsequent handling thereof.

Referring now to FIGS. 3 and 4 in particular, it will be seen that thereis illustrated a modified form of laminate which is generally referredto by the numeral 15. The. laminate 15 is of a two layer construction asopposed to the three layer construction of the laminate 5 and includes ametal foil layer 16 which is suitably bonded to a plastic layer 17. Inother words, the laminate 15 may be identical with the laminate 5 withthe exception of the omission of one of the metal foil layers. -In orderto facilitate the opening of a container formed from the laminate 15,the laminate 15 is provided with a removable tear strip 18. The tearstrip 18 is defined by a pair of weakening lines 19 and 20 formed in theplastic layer 17.

It will be readily apparent from FIG. 4 that the weakening lines 19 and20 may be formed by merely applying'a hot knife edge'to the layer 17along the desired line of weakening. The hot knife edge will effect ascoring of the layer 17 by the fusing of the material of the layer 17touched by the hot knife edge when the material is a thermoplasticmaterial or by the'charring or other thermodegradation of otherthermodegradable materials.

It will be understood that a container formed of the laminate 15 may beopened in the same manner as that described above with respect to thelaminate 5. The only difference between the laminates 5 and 15 is thatthe laminate 5 is of a three-ply construction and includes an innerlayer ofmetal foil as well as-an outer layer of metal foil whereas thecontainer formed from the laminate 15 includes only .one layer of metalfoil. Also, it will be readily apparent that since the layer 17 isexposed on one side, it is not necessary to effect the weakening of thematerial of the plastic layer 17 through an overlying metal foil layer.Therefore, the metal foil layer 16 is not creased or folded along theweakening lines 19 and 20.

Tests have been made with both the three-ply laminate 5 and the two-plylaminate 15 utilizing foil and plastic layer, thicknesses within thecommercially feasible range of packaging materials. It will'be readilyapparent that 'one'of theprimary restrictions is the tear strength ofthe 'inch wherein the metal foil is formed of full hard temper aluminumhaving a thickness of 0.005 inch and the plastic layer is "low densitypolyethylene having a thickness of 0.011 inch. It is obvious, however,that these are not the maximum limits for "a two-ply laminate.

Limited tests have been made with three-ply laminates"utilizing'aluminum foil and low density polyethylene.

Utilizing both dead soft temper and full hard temper aluminum'foil,laminates having a thickness of 0.002 inch have proved to be successfulwith the foil thickness being 0.005- inch and the plastic layerthickness being 0.001 inch. Utilizing full hard temper aluminum foilhaving a thickness of 0.0035 inch with a plastic layer of a thickness'of0.0055 inch, a commercially feasible laminate having a thickness of0.0125 inch has been formed. Again this latter mentioned laminate is notintended to be an example of the upper feasible limits of the laminate.

Although laminates formed of aluminum foil and low "density polyethylenemay at the present be the most feasible commercial laminates, theinvention is not restricted to such laminates either as to the foil orthe plastic layer. Numerous other thermoplastic resins could be utilizedin the laminates, including polystyrene, Mylar and polyvinyl resins.Although aluminum alloys will tear readily, it is also feasible toutilize iron for the forming of the foil, particularly with the heavierthickness foils and the iron may be plain CMQ (can makers quality) blackplate or black plate which has been tinplated or provided with aprotective enamel coating on at least one side thereof. Also, moreexpensive metals, such as brass, copper, tin, etc. may be utilized.Cellophane and paper have been found to have suitable thermodegradableproperties for use in accordance with this invention as materials forthe forming of the thermodegradable layers.

It has been found that when the non-metallic layer of a laminate formedin accordance with this invention is formed of thermoplastic material,minute ribs are formed adjacent the score line. For example, in FIG. 4,minute ribs 21 are formed on opposite sides of the score line 20 in thethermoplastic layer 17. When the layer 8 is formed of thermoplasticmaterial, similar ribs will be formed. These ribs facilitate the guidingof the tearing of the laminate and thus further assure the straight linetearing along the predetermined weakening line.

With respect to the two-ply laminates, when the thermodegradable layeris on the interior of a package and the package is to be utilized withreactive materials includ-. ing foods, care must be made in selectingthe thermodegradable material. For example, when food is to be packagedwithin a container formed from the two-ply laminate, the thermoplasticresins selected for use as the plastic layer should be one which doesnot contain a flavor afiecting volatile.

It will be readily apparent that other metals and materials may beutilized in the forming of the metal foil and the non-metal layer of thelaminates within the spirit and scope of the invention, as defined bythe appended claims.

I claim:

1. In a laminate, a weakening line construction, said laminate beingformed solely of one metal foil layer and one thermoplastic resinstiifening layer, and said thermoplastic resin layer having a weakeningline molded in the surface thereof remote from said foil layer.

2. A laminate having a predetermined tear line, said laminate comprisingat leaast one metal foil barrier layer and a stilfening layer ofthermodegradable material, and a weakening line formed in saidstiffening layer along said tear line by the thermal degradation of saidstifiening layer and said thermodegradable material is cellophane.

3. A method of forming a tear line in a laminate including a stiffeninglayer formed of thermodegradable material comprising the steps ofproviding a tool having a heated edge, applying the heated edge to thelaminate under pressure to effect a heating and degradation of thestiffening layer, and effecting a relative movement of said laminate andsaid tool along a predetermined line to form a weakening line in thestiffening layer.

4. The method of claim 3 wherein the stilfening layer is exposed and thetool is applied directly thereto.

5. A method of forming a tear line in a laminate including a stiffeninglayer of thermoplastic resin comprising the steps of providing a toolhaving a heated edge, applying the heated edge to the laminate underpressure to effect a heating and flowing of the stiffening layer, andeffecting a relative movement of said laminate and said tool along apredetermined line to form a weakening line in the stiffening layer.

References Cited UNITED STATES PATENTS 2,830,001 4/1958 Barnes et al161-119 X 2,891,713 6/1959 ONeil 229-51 TS 2,213,758 9/ 1940 Eichberg etal 22951 C 2,554,160 5/1951 Von Gunten 229-51 ST 2,710,046 6/1955 Markuset al. 161-40 2,991,000 7/1961 Spees 229-51 AS 3,186,628 6/ 1965 Rohde229-51 TS WILLIAM A. POWELL, Primary Examiner US. Cl. X.R.

